1. Field of the Invention
This invention relates to a structure of an integrated circuit, and more particularly, to a structure of an integrated circuit providing a connection of metal lines in the integrated circuit, by which can reduce the stress and adhesion generated by the metal lines of the multi-layered structure of the integrated circuit.
2. Description of Related Art
During the fabricating process of the integrated circuit, bonding pads are commonly formed for interface between an internal circuit of the integrated circuit and an external circuit. By the formed bonding pads and the metal plugs formed in dielectric layers, the external circuit can make electrical connection with the internal circuit of the integrated circuit.
Referring to FIG. 1, it shows a cross-sectional view of a conventional structure of the bonding pad and the internal circuit in the integrated circuit. An internal circuit area 110 and a bonding pad area 120 are simultaneously formed on the substrate 100. The structure comprises a field oxide layer 10, a gate oxide layer 11, a gate 12, source/drain regions 13, oxide layer 14, a first metal layer 16, a inter metal dielectric layer 17 and a second metal layer 18.
The portion of the second metal layer 18 in the bonding area 120 is used for a bonding pad, by which the external circuit (not shown) can electrically connected to the internal circuit area 110 through via 19. In addition, for avoiding the first metal layer 16 punches through the conjunction of the source/drain region 13 to cause the leakage effect, a barrier layer 15 is formed under the first metal layer 16 to serve as a barrier. The barrier layer 15 is composed of, for example, titanium, TiN or TiW. If adhesion between the barrier layer 15 and the oxide layer 14 served as a isolation layer is bad, and a coefficient of expansion of the metal layer is different from that of the oxide layer, stress is generated in the following manufacturing process, and then peel phenomenon is introduced in this area.
Some technique for reducing the generated stress and the peel phenomenon is developed in the prior art, in which provides a different layout and design structure. As described in U.S. Pat. No. 5,700,735, it provides a structure of a bonding pad for increasing the adhesion for avoiding peeling. The other conventional technique is shown in FIGS. 2A-2C, which discloses a multi-layered structure for reducing stress generated therebetween.
Referring to FIG. 2A, it shows a cross-sectional view of a structure of a bonding pad in a device. The first metal pad 34 is formed over a first dielectric layer 40 and covered by a second dielectric layer 44. The second metal pad 32 is formed over the second dielectric layer 44 and covered by the third dielectric layer 48. The third metal pad is formed over the third dielectric layer 48 and surrounded by the forth dielectric layer 52. A plurality of first plugs 38 are formed between the first metal pad 34 and the second metal pad 32. A plurality of second plugs 36 are formed between the second metal pad 34 and the third metal pad 30. For testing the stress generated in the multiple layers, a test fixture 20 is connected to the third metal pad 30. The test fixture 20 can be used for testing either a tensile force 22 or a shear force 24.
As above-described structure, the real structure in the device is not so smooth as shown in FIG. 2A. The location of the first plugs 38 is relatively rotated 45 degrees compared with the location of the second plugs 36, which the first plugs 38 and the second plugs 36 are staggered to each other. It can avoid the situation that the plug can not contact the metal pad. In addition, the above-described structure can not solve the problem caused by the stress between the metal layer and the oxide layer which serves as the dielectric layer, that is, the peeling problem still exists. The peeling problem is mainly caused by the stress generated in the interface during the following fabricating process. A method that can eliminate the phenomenon is improving the design of the structure to release the generated stress.
Referring to FIG. 2B, it shows a cross-sectional top view of the second plugs 38 in a direction indicated by a dash line 2B-2B' shown in FIG. 2A. The cross-sectional view of the first plugs 36 are represented by a dash line 2C-2C'.